α-, β- and γ-Cyclodextrins (α-CD, β-CD and γ-CD) are cyclic oligosacharides consisting of 6, 7 or 8 glucopyranose units, respectively, which are joined together by α(1–4) linkages: 
Cyclodextrins (termed hosts) can imbibe certain molecules or parts thereof (termed guests) into their center cavities. The noncovalent reversible adducts or inclusion complexes formed between the host and the quest can drastically change the properties of the parent guest molecules in diverse ways, such as to increase solubility, decrease volatility, protect from chemical or light-catalyzed reactions, change the location of absorption of complexed drugs in the intestine, etc.
Parent CDs can be covalently modified with a number of reagents to form chemical derivatives. The derivatives can normally bind similar guest compounds as do the parent CDs, but the properties of the complexes can be changed, A description on the syntheses of CD derivatives and the properties of inclusion complexes of both parent and modified cyclodextrins can be found for instance in Croft, A. P. & Bartsch, R. A. “Synthesis of Chemically Modified Cyclodextrins”, Tetrahedron, 1983, V. 39, No 9, P. 1417–1471 Szejtli, J. “Cyclodextrin Technology”, Kluwer Academic Publishers, Dordrecht, 1988, pp. 1–450.
Some derivatives of β-CD have a higher solubility than do the parent compound and hence they are often preferable complexants and solubilizers. The potential of the chemical derivatives of β-CD is amplified by its low price as a starting material in comparison to α- and γ-CDs. In contrast to β-CD, the more expensive α- and γ-CDs are readily water soluble and can be used without chemical derivatization for certain purposes. This is illustrated by a number of reports on their complexes with various guest compounds such as steroid hormones, cholesterol or its derivatives and with some drugs. Appropriately alkylated or hydroxyalkylated γ-CDs are also good complexants since their inclusion complexes do not precipitate even at high concentration, as stated in EP 06792.
A large number of papers deals with the syntheses of CD chemical derivatives and their application for divergent purposes (see e.g. Szejtli, J “Cyclodextrin Technology” 1988) clearly showing the importance of the CD derivatives.